Fire control

To control the fire of a long-range artillery unit, radio communication is used. However, since the communication occurs under conditions where the enemy creates radio interference, in order to ensure the reliability of message transmission (which is an integer from $0$ to $1000000$), it is encrypted as follows: each digit is transmitted, and then immediately repeated as many times as its value. For example, the digit $3$ is transmitted four times, $0$ — once, etc., so instead of the message $103$, the transmitted message is $1103333$.

Write a program that implements this encryption.